The present invention relates to a laminated phase plate for use in direct-viewing-type liquid crystal display devices used for office machinery including word processors and notebook-sized personal computers, various types of visual equipment and game equipment, a projection-type liquid crystal display device which displays an enlarged image by projecting an image of a reflective liquid crystal display illuminated by light source, and liquid crystal display devices such as a head-mount display which is fixed at the head of a viewer, and also relates to liquid crystal display devices incorporating the laminated phase plate.
Conventionally, an optical phase difference compensation plate composed of an oriented polymer film has been used for various applications. Examples of the optical phase difference compensation plates includes a xc2xc waveplate for giving a phase difference of {fraction (xcfx80/2)} between two linearly polarized lights having vibration planes perpendicular to each other, and a xc2xd waveplate for giving a phase difference of xcfx80 between them. Since the phase differences of these optical phase difference compensation plates originated from their retardation vary according to the wavelength of light, it was difficult to provide a uniform polarization state, which is obtained as a result of a phase difference, for lights of different wavelengths by a structure including only a single optical phase difference compensation plate.
In order to solve such a drawback, Japanese laid-open patent publication No. (Tokukaihei) 5-100114 discloses a xc2xd waveplate produced by a combination of a polarizer and a plurality of xc2xd waveplates, and a circular polarizer obtained by further adding a xc2xc waveplate to the combination.
In the former structure of these structures, by combining xc2xd waveplates, a condition for giving a phase difference of xcfx80 to light whose linearly polarized component has been selectively transmitted by the polarizer is ensured within a wide wavelength range. On the other hand, in the latter structure, a condition for giving a phase difference of {fraction (xcfx80/2)} is ensured within a wide wavelength range by adding a xc2xc waveplate to the above-mentioned structure. As a result, light having a wavelength within a range satisfying the xc2xd wavelength condition for giving a phase difference of xcfx80 becomes linearly polarized light oriented in a different direction from linearly polarized light prepared by a polarizer. With this structure, it is possible to produce linearly polarized light having a uniform vibration plane for wavelengths satisfying the xc2xd wavelength condition.
Moreover, as a color display, a liquid crystal display device having thin and light weight characteristics has been put to practical use. At present, a transmissive type liquid crystal display device using a light source as an illumination from behind has been most widely used as a color display device, and the application thereof has increased to various fields because of the above-mentioned characteristics.
A reflective type liquid crystal display device does not require a backlight for display, and therefore it can lower the power consumption by cutting the power for the light source and reduce the space and weight by the space and weight of the backlight as compared with the transmissive type liquid crystal display device. In other words, the reflective type liquid crystal display device can achieve a reduction in the power consumption, and is suitable for use in apparatuses aiming at reductions in their thickness and weights.
Furthermore, regarding the contrast characteristic of the display screen, in a light emitting type display devices as CRTs, a substantial degradation in the contrast ratio, i.e., a so-called washout, occurs outdoors in daylight. Besides, in this aspect, even in a transmissive type liquid crystal display device to which a low reflection treatment was applied, a lowering of visibility is unavoidable in an environment in which ambient light such as direct sunlight is extremely strong compared with display light.
On the other hand, in the reflective type liquid crystal device, since display light proportional to the amount of ambient light is obtained, the reflective type liquid crystal device is particularly suitable for use as a display section of apparatuses used in outdoor, such as personal digital tools, digital still cameras, and portable comcorders.
However, although the reflective type liquid crystal display device has such very advantageous application fields, it does not have a sufficient contrast ratio and reflectivity, and performances for achieving multicolor display, high definition display, moving image display, etc. Therefore, a reflective type color liquid crystal display device having sufficient practical characteristics has not been realized so far.
The following description will explain a reflective type liquid crystal display device in detail.
Since a conventional twisted nematic (TN) liquid crystal element is constructed with the use of two polarizers, the contrast ratio and the viewing angle characteristic are improved. However, since a liquid crystal modulation layer and a light reflecting layer is separated from each other by a distance equal to the thickness of a substrate, etc., parallax occurs due to the difference between a light path along which illumination light is incident and a light path along which the light is outgoing. Thus, in particular, a structure in which the twisted nematic liquid crystal element is used for a normal conventional transmissive type liquid crystal display using a combination of a single liquid crystal modulation layer and color filters which apply a plurality of color elements to different pixels is not suitable for a high resolution, high definition color display device. The reason for this is that, when the traveling direction of light passing through a color element during the incidence of light and that of light passing through a color element after the light is reflected tilt with respect to each other, the light path varies according to the tilt direction and tilt angle. For such a reason, a color display of a reflective type liquid crystal display device using this display mode has not been put to practical use.
Meanwhile, a guest-host (GH) type liquid crystal display element in which no polarizer or one polarizer is used and dye is added to a liquid crystal has been developed. However, the guest-host type liquid crystal element suffers from problems that the reliability is not sufficient due to the addition of dye and a high contrast ratio is not obtained because the dichroism ratio of the dye is low. In particular, in a color display using color filters, since the reflected light of the pixel in the dark state is observed together with the reflected light of the pixel in the bright state, the color purity is substantially lowered by such an insufficient contrast. In order to prevent the degradation of color purity, it is necessary to apply color filters of high color purity. However, when color filters of high color purity are used, the brightness is lowered. Thus, there is a conflict between the lowering of brightness and an advantages of the GH technique of achieving a high brightness without using a polarizer because this advantage is spoilt.
In view of the above-mentioned circumstances, liquid crystal display devices employing a structure in which one polarizer which is expected to achieve a high resolution, high contrast display (hereinafter referred to as the single polarizer structure) have been developed. As one example, a reflective (450 twisted type) TN type liquid crystal display device using one polarizer and xc2xc waveplates is disclosed in Japanese laid-open patent publication No. (Tokukaisho) 55-48733.
According to this prior art, a layer of liquid crystal twisted at 45xc2x0 is used, and the vibration plane of incident linearly polarized light is switched between two states, i.e., a state in which the vibration plane is parallel to the optical axis of the xc2xc waveplate and a state in which the vibration plane is oriented in a direction which differs from the direction of the optical axis by 45xc2x0 by controlling an electric field applied to the liquid crystal layer so as to achieve a black and white display. This liquid crystal cell is constructed by arranging a polarizer, a 45xc2x0-twisted liquid crystal cell, a xc2xc waveplate, and a reflector in this order from the incident side.
Additionally, the present inventors filed a patent application directed to a reflective type homogeneous structure realized by a combination of one polarizer, homogeneous alignment liquid crystal cell, and optical phase difference compensation plate (see Japanese laid-open paten publication No. (Tokukaihei) 6-167708). In this display mode, a homogeneous (no twisted planer) alignment liquid crystal layer and one optical phase difference compensation plate are placed between a reflector disposed on the inner surface of the liquid crystal cell and a polarizer provided on the outside of the liquid crystal cell (and optical phase difference compensation plate). In this structure, the light paths comprising the incident light path and outgoing light path pass through the polarizer only twice, and also pass through a transparent electrode, which is formed on one of glass substrates (upper substrate) of the cell and can not avoid light absorption, only twice. Therefore, with this cell structure, a high reflectivity can be obtained.
Furthermore, a structure in which a layer of twisted nematic liquid crystal is placed between a reflector (disposed on the inner surface of the cell) and one polarizer is disclosed in Japanese laid-open patent publication No. (Tokukaihei) 2-236523 and Japan Display ""89, p. 192.
The following descriptions will explain the theory of such a single polarizer display as disclosed in Japanese lain-open patent publication Nos. (Tokukaihei) 6-167708 and 2-236523, and Japan Display ""89, p. 192.
A polarizer disposed on the incident side transmits only linearly polarized components in one direction among linearly polarized components of incident light and outgoing light, and absorbs linearly polarized components in the directions perpendicular to the transmissive directions. The incident light which has been transmitted through the polarizer is changed in its polarization state by an optical phase difference compensation plate such as a {fraction (xcex/4)} waveplate and then incident on a liquid crystal layer (in the case of Japanese laid-open patent publication No. (Tokukaihei) 6-167708), or incident on the liquid crystal layer without a change in the polarization state (in the cases of Japanese laid-open patent publication No. (Tokukaihei) 2-236523 and Japan Display ""89, p. 192). When the light incident on the liquid crystal layer passes through the liquid crystal layer, the polarization state thereof changes and the light reaches a reflector. The light which has reached the reflector passes through the liquid crystal layer and {fraction (xcex/4)} waveplate in reversed order to the order when it was incident, while changing in the polarization state, and reaches the polarizer again.
At this time, the final ratio of the polarized components in the transmitting direction of the polarizer determines the overall reflectivity of the liquid crystal layer. More specifically, the brightest display is obtained when the polarization state of the outgoing light just before passing through the polarizer is linear polarization in the transmitting direction of the polarizer, and the darkest display is obtained when the polarization is linear polarization in the absorbing direction.
The necessary and sufficient conditions for achieving these states with light which is normally incident on and outgoing from a liquid crystal display device are known as described below, but the detailed explanation thereof is omitted. In other words, the necessary and sufficient conditions are such that the polarization state on the reflector is linear polarization in any direction for the bright state, and the polarization state on the reflector is right- or left-handed circular polarization for the dark state. The above-mentioned conditions presume specular reflection without polarization scramble. In other words, with reflection which scrambles polarization, the brightness in the bright state is lowered, while the brightness in the dark state is increased, resulting in a degradation of the display contrast. Therefore, the reflection with polarization scramble is not suitable for the single polarizer structure aiming for a high contrast.
A reflective type liquid crystal display device in which one polarizer and a liquid crystal layer having a negative dielectric anisotropy and homeotropic alignment is disclosed. U.S. Pat. No. 4,701,028 (Clerc et al.) discloses a reflective type liquid crystal display device incorporating a combination of one polarizer, xc2xc waveplate, and homeotropically aligned liquid crystal cell. Moreover, Japanese laid-open patent publication No. (Tokukaihei) 6-337421 discloses a reflective type liquid crystal display device incorporating a combination of one polarizer, xc2xc waveplate, and hybrid aligned liquid crystal cell. Furthermore, a reflective type liquid crystal display device incorporating a combination of one polarizer, xc2xc waveplate, and homeotropically aligned liquid crystal cell is disclosed in Euro Display ""96, p. 464.
These devices are liquid crystal display devices which use a xc2xc waveplate, realize a dark state by making the retardation of the liquid crystal layer substantially zero in the absence of applied voltage and maintaining the polarization state, and produce a bright state by applying a voltage so that the retardation of liquid crystal layer has a finite value, i.e., liquid crystal display devices of a so-called normally black mode in which switching is executed using the retardation.
On the other hand, a projection type liquid crystal display device has a mechanism for enlarging and projecting a display image produced by liquid crystal elements, and provide a large-area display by a small device compared with the size of the display image. Therefore, the projection type liquid crystal display device has been used widely in practical image display devices such as large display devices and data projectors.
In addition, a head-mount display is a small device, and has such characteristics that it effectively provides a large display screen to a viewer, occupies the field of view of the viewer because it is fixed at the head, and provides independent display information to right and left eyes. The application of the head-mount display to virtual reality techniques, high quality image displays, three-dimensional picture reproduction-use displays, etc. in future is expected because of the above-mentioned merits.
Among these projection type liquid crystal display device and head-mount display, a reflective type liquid crystal display device has an advantage that it enables the production of a device with a multi-functional driving substrate by fabricating the liquid crystal element and peripheral circuits into the same device and extracting the light incident on the liquid crystal element from the illuminated surface of the device. In other words, the above-mentioned reflective type liquid crystal display device has an advantage that the non-light-transmitting substrate such as silicon wafer is usable, and an advantage that active elements for driving the liquid crystal layer and wiring can be designed without deteriorating the utilization efficiency of light even when the liquid crystal display element is designed in a small size.
Alternatively, it is possible to employ a technique such as a so-called liquid crystal light valve. With the use of the liquid crystal light valve, display information is written by illuminating light from a side opposite to the light projection side of the substrates holding the liquid crystal element therebetween. With this structure, the resistance of a photoconductive layer is changed, the voltage is allocated with respect to the liquid crystal layer to which a voltage has been applied during the application of the voltage to the photoconductive layer, and the strength of the projected light is varied according to the writing light. It is thus possible to apply the above-mentioned reflective type liquid crystal display to the projection type devices. In particular, the efficiency of light is important because it determines the overall brightness of the device.
Besides, since there is a possibility that ambient lighting environments in observing the display of such a projection type liquid crystal display device or head-mount display are very dark, a high quality display is required. Hence, in order to achieve a high contrast display by realizing a good black display in such lighting environments, high light blocking properties are required for the black display.
Moreover, Japanese laid-open patent publication No. (Tokukaihei) 8-62564 discloses a technique as an example of a liquid crystal projection type liquid crystal display which is fabricated using a polarizing beam splitter and achieves a high contrast display with the use of an optical phase difference compensation plate. According to the structure disclosed in this publication, in order to achieve a high contrast display, an optical element (birefringence element) for producing a phase difference is used so as to compensate for the phase difference of the liquid crystal layer in the dark state.
In a structure in which a homogeneous liquid crystal cell is used in a single polarizer liquid crystal display device of the above-mentioned prior art, when a bright state is provided by the application of a voltage or when a bright state is provided by an alignment state in a homeotropic liquid crystal cell in which the birefringence of the liquid crystal layer substantially disappears in the absence of applied voltage, it is preferred to satisfy the following. Specifically, it is preferred that a polarization state after the outgoing of the light from the optical phase difference compensation plate to liquid crystal layer is made linearly polarized light by a combination of the polarizer of the liquid crystal display device achieving a good bright state in a wide wavelength range and the optical phase difference compensation plate. However, when the linearly polarized light has a fixed plane of vibration in every wavelength range, the function of the liquid crystal layer of compensating the differences in the functions of the polarization states in the respective wavelengths is not achieved.
If the above-mentioned two conditions, i.e., light of each wavelength is linearly polarized light and a polarization state where the direction of the vibration plane varies depending on the wavelength, are satisfied, the phase plate can be used as an optical phase difference compensation plate which can serve as a color compensation plate aiming for the optical compensating function of the liquid crystal layer.
According to the one disclosed in the above-mentioned Japanese laid-open patent publication No. (Tokukaihei) 5-100114, a method for obtaining a xc2xd wavelength condition for a wide wavelength range is provided. However, polarized lights of different wavelengths have vibration planes of the same direction, and the resultant polarization state differs only in the direction from the polarization state immediately after the passage through the polarizer. In other words, the polarization direction does not vary depending on the wavelength.
Moreover, in the descriptions of the above publication, it is also disclosed that lights in a wide wavelength range is made circularly polarized lights by a method of providing a xc2xc wavelength condition for a wide wavelength range. However, this publication does not disclose a method of providing linearly polarized light of a direction varying according to the wavelength.
In a liquid crystal display device disclosed in the above-mentioned Japanese laid-open patent publication No. (Tokukaisho) 55-48733, it is necessary to provide a xc2xc waveplate between the liquid crystal layer and the reflector. Therefore, it is difficult in theory to form a reflective film on the inner side of the liquid crystal cell. Thus, this liquid crystal display device is not suitable for a high resolution, high definition display.
Besides, in a reflective homogeneous structure as disclosed in the above-mentioned Japanese laid-open patent publication No. (Tokukaihei) 6-167708, coloration occurs because of the wavelength dispersion between the liquid crystal cell and optical phase difference compensation plate. In such a conventional structure, the dark state tends to color. Thus, there is a problem that a black-and-white display can not be achieved.
Similarly, in the homeotropic structure as disclosed in the above-mentioned Japanese laid-open patent publication No. (Tokukaihei) 6-337421 and Euro Display ""96, p. 464, the liquid crystal is aligned parallel without being twisted during the application of a voltage. Hence, the dark state tends to color because of the effect of the wavelength dispersion between the liquid crystal cell and optical phase difference compensation plate. Consequently, there is a problem that a good black-and-white display cannot be achieved. Moreover, when the viewer sees the display in the absence of applied voltage from a directly front direction of the substrate (i.e., from a direction normal to the substrate), it is possible to achieve a good dark display because of zero retardation. However, when the viewer sees the display from a direction tilted from the direction normal to the substrate, retardation occurs. Therefore, the viewing angle characteristics related to the tilt angle of the display are very bad, and a good dark display is not achieved.
On the other hand, the structures as disclosed in Japanese laid-open patent publication No. (Tokukaihei) 2-236523 and Japan Display ""89, p. 192 have higher reflectivity in the bright state compared with a structure using two polarizers. However, since the transmissivity in the dark state depends greatly on the wavelength, a good black display is not achieved. Additionally, And that is the product of a difference of refractive indices (xcex94n) of the liquid crystal layer and a thickness (d) of the liquid crystal layer needs to have a very small value of around 200 nm. When And has such a value, if a liquid crystal panel is fabricated using a general liquid crystal material, i.e., a liquid crystal material having An of 0.065 or more, the cell gap in the liquid crystal layer has a very small value of substantially 3 xcexcm. Thus, it is difficult to manufacture the liquid crystal panel.
Furthermore, the structure disclosed in the above-mentioned Japanese laid-open patent publication No. (Tokukaihei) 8-62564 using a polarizing beam splitter and a birefringence element was designed to improve the contrast. However, since the brightness was not improved, the efficiency was not increased. Moreover, according to the descriptions in an embodiment disclosed in this publication, although the contrast was improved, the brightness was lowered and therefore the efficiency was rather worsened. According to an example described in the embodiment of this publication, in order to improve the projection efficiency, the liquid crystal alignment which is oriented homeotropically when a low voltage is applied is arranged to be a tilted alignment state by increasing the applied voltage so as to increase the brightness in this alignment state. However, in order to maintain the contrast, there is a requirement that an optical element used for this arrangement does not increase the brightness in the dark state. However, an optical element having such a function and the liquid crystal display device incorporating the optical element have never been disclosed.
In order to solve the above problems, i.e., the problems associated with a single polarizer liquid crystal display device capable of providing high resolution displays, or the problems associated with a reflected light projection type liquid crystal display device and head-mount display, objects of the present invention are to improve the function of a laminated phase plate, provide a laminated phase plate capable of achieving a reflective type liquid crystal display device with an excellent visibility or a projection-type liquid crystal display device with a high efficiency, and a liquid crystal display device incorporating the laminated phase plate.
In order to achieve the above objects, a laminated phase plate of the present invention is formed by laminating a first optical phase difference compensation plate and a second optical phase difference compensation plate. The first optical phase difference compensation plate has a retardation between 100 nm and 180 nm for transmitted light of a wavelength of 550 nm in a direction normal to the first optical phase difference compensation plate. The second optical phase difference compensation plate has a retardation between 200 nm and 360 nm for transmitted light of a wavelength of 550 nm in a direction normal to the second optical phase difference compensation plate. The first and second optical phase difference compensation plates are arranged so that, when linearly polarized light which is visible light and has a fixed plane of vibration is incident on the second optical phase difference compensation plate, the value of |xcex81xe2x88x922xc3x97xcex82|, wherein xcex81 is an angle between a direction perpendicular to the direction of vibration of the linearly polarized light or the direction of vibration of the linearly polarized light incident on the set off plates and a direction of a slow axis of the first optical phase difference compensation plate, and xcex82 is an angle between the direction perpendicular to the direction of vibration of the linearly polarized light or the direction of vibration of the linearly polarized light incident on the set off plates and a direction of a slow axis of the second optical phase difference compensation plate, is within a range between 80 degrees and 100 degrees.
The above invention was implemented by finding that, in a combination of an optical phase difference compensation plate which produces a phase difference of a xc2xd wavelength and an optical phase difference compensation plate which produces a phase difference of a xc2xc wavelength, it is important that the directions of the optical phase difference compensation plates are set to specific directions.
With the use of the laminated phase plate of the present invention, it is possible to achieve a liquid crystal display device in which a reflecting film formed surface of a reflector is located adjacent to a liquid crystal layer, and to provide a good dark state. Therefore, a reflective type liquid crystal display device capable of providing a high contrast, high definition display of a moving picture without parallax can be obtained. Moreover, if the laminated phase plate of the present invention is adopted into a liquid crystal display device for projecting reflected light or into a head-mount display, the projection efficiency can be improved.
In addition, in order to achieve the above object, a liquid crystal display device of the present invention includes a first substrate, a second substrate having light transmitting properties, a liquid crystal layer which is made of a liquid crystal compound containing liquid crystal and disposed between the first and second substrates, the laminated phase plate of claim 1 disposed on a display side of the second substrate, polarizing means, disposed on the second optical phase difference compensation plate side of the laminated phase plate, for causing linearly polarized light which is visible light and has a fixed plane of vibration to be incident on the second optical phase difference compensation plate, and light reflecting means, when the linearly polarized light which is visible light and has a fixed plane of vibration is caused to be incident on the second optical phase difference compensation plate by the polarizing means, for reflecting at least a part of the light which has transmitted through the second optical phase difference compensation plate, first optical phase difference compensation plate, second substrate and liquid crystal layer and gone out of the liquid crystal layer.
The above-mentioned invention was implemented by finding a structure of a liquid crystal display device which uses the laminated phase plate of the present invention most effectively for a display when the liquid crystal display device is constructed with the use of the laminated phase plate of the present invention.
The liquid crystal display device of the present invention achieves a reflective type liquid crystal display device with a high reflectivity and high contrast. Besides, the reflective film formed surface of the reflector can be located on the liquid crystal layer side of a transparent substrate, and thus a good dark state can be achieved. It is therefore possible to provide a high contrast, high definition display of a moving picture without parallax. Additionally, when a polarizing beam splitter is used for a liquid crystal display device having a layer of liquid crystal homeotropically aligned, an especially excellent contrast characteristic is obtained.
Moreover, when a color filter which has been adjusted for high brightness is used in a liquid crystal display device of the present invention, it is possible to achieve a reflective type color liquid crystal display device that provides high display quality with good color reproduction characteristics.
Furthermore, another invention is a liquid crystal display device (liquid crystal display device {circle around (1)}) which is based on the liquid crystal display device of the present invention, and in which the polarizing means is formed by a polarizer.
According to the liquid crystal display device {circle around (1)}, it is possible to achieve a direct viewing type liquid crystal display device which can most effectively use the laminated phase plate of the present invention. In other words, according to the liquid crystal display device {circle around (1)}, it is possible to provide a liquid crystal display device which achieves a good black display and good brightness with the laminated phase plate, and exhibits a good display characteristic that does not deteriorate the brightness.
Still another invention is a liquid crystal display device (liquid crystal display device {circle around (2)}) which is based on the liquid crystal display device of the present invention or the liquid crystal display device {circle around (1)}, and in which the liquid crystal compound has a positive dielectric anisotropy, the twist angle of the liquid crystal between the first and second substrates is between 60 degrees and 100 degrees, and the product of a difference of refractive indices of the liquid crystal of the liquid crystal layer and the thickness of the liquid crystal layer is between 150 nm and 330 nm.
According to the liquid crystal display device {circle around (2)}, it is possible to optimize the liquid crystal display device of the present invention or liquid crystal display device {circle around (1)}. In other words, according to the liquid crystal display device {circle around (2)}, it is possible to ensure sufficiently low reflectivity in a dark state for a visible wavelength range, and provide a liquid crystal display device which can be manufactured easily at a high yield.
Yet another invention is a liquid crystal display device {circle around (3)} which is based on any one of the liquid crystal display device of the present invention and liquid crystal display devices {circle around (1)} and {circle around (2)}, and in which the light reflecting means is a light reflecting film which is made of a conductive material, placed on the liquid crystal layer side of the first substrate, and has a surface with smoothly and continuously changing undulations.
In the direct viewing type liquid crystal display device, when the bright state is a white state rather than a mirror reflection, it is necessary to perform a diffuse reflection. According to the liquid crystal display device of the present invention, especially a liquid crystal display device with excellent display quality can be realized by the use of a reflector having smooth undulations.
More specifically, the liquid crystal display device {circle around (3)} was implemented by finding a structure of the light reflecting means, which is particularly suitable for the liquid crystal display device of the present invention. According to the liquid crystal display device {circle around (3)}, since the light reflecting film having undulations is provided, it is possible to prevent the reflection by the light reflecting means from becoming a mirror reflection. Consequently, it is possible to prevent the image in the surroundings of the device, such as the face of the viewer, from being reflected in the display surface of the liquid crystal display device, thereby realizing an excellent white display. Moreover, since no element having a scattering effect is disposed in front of the liquid crystal display device, it is possible to achieve an excellent black display. Accordingly, a liquid crystal display device with a high contrast ratio can be realized.
Besides, according to the liquid crystal display device {circle around (3)}, since the light reflecting film is formed by a conductive material, it also performs a function of an electrode for applying a voltage to the liquid crystal layer with a transparent electrode formed on the second substrate.
In order to achieve the liquid crystal display device {circle around (3)}, a plurality of protruding portions are formed on the liquid crystal layer side of the first substrate so that undulations are formed by the protruding portions and the first substrate, a planerization film for smoothing the surface of the undulations is formed on the protruding portions, and the light reflecting film is formed on the planerization film.
Yet another invention is a liquid crustal display device (liquid crystal display device {circle around (4)}) which is based on the liquid crystal display device {circle around (3)}, and in which a surface having the undulations of the light reflecting film has anisotropic properties that depend on the direction in the plane of the first substrate.
According to the liquid crystal display device {circle around (4)}, it is possible to further improve the reflection brightness of the reflecting type liquid crystal display device.
The liquid crystal display device {circle around (4)} can be realized by changing the average interval of the undulations of the undulating surface of the light reflecting film according to the direction in the plane of the first substrate.
More specifically, the liquid crystal display device {circle around (4)} includes a plurality of protruding portions and a planerization film between the light reflecting film and the first substrate as described above, and the protruding portions when seen from a direction normal to the first substrate have elliptical shapes whose longer axes are oriented in the same direction.
Still another invention is a liquid crystal display device (liquid crystal display device {circle around (5)}) which is based on any one of the liquid crystal display device of the present invention and liquid crystal display devices {circle around (1)} to {circle around (4)}, and in which the liquid crystal layer has a liquid crystal whose alignment direction varies according to an applied voltage, and dispersed polymer which has optical anisotropy and an alignment direction that does not vary according to the applied voltage.
In the liquid crystal display device {circle around (5)}, the liquid crystal and polymer are dispersed in the layer of the aligned liquid crystal, and the polymer has an alignment direction similar to that of liquid crystal molecules in the absence of applied voltage and optical anisotropy by itself. Accordingly, in the absence of applied voltage, the refractive index of the liquid crystal compound and that of the polymer are the same, and thus scattering does not occur. On the other hand, when a voltage is applied, the refractive index of the liquid crystal compound and that of the polymer differ from each other, and scattering occurs. Therefore, even with the use of a reflective film exhibiting a mirror surface, it is possible to provide a white display without mirror reflection in a direction other than the specular reflection, thereby achieving an extremely high contrast ratio.
In addition, still another invention is a liquid crystal display device (liquid crystal display device {circle around (6)}) which is based on the liquid crystal display device of the present invention, and in which the polarizing means is formed by a polarizing beam splitter.
The liquid crystal display device {circle around (6)} was implemented by finding that when a polarizing beam splitter was used as the polarizing means in a projection type or head-mount type liquid crystal display device with reflected light, the brightness in the dark state was not increased with the use of the optical phase difference compensation plate of the present invention.
According to the liquid crystal display device {circle around (6)}, it is possible to realize a projection type or head-mount type liquid crystal display device that maintains a high contrast ratio.
Furthermore, yet another invention is a liquid crystal display device (liquid crystal display device {circle around (7)}) which is based on the liquid crystal display device {circle around (6)}, and in which the liquid crystal compound has a positive dielectric anisotropy, the twist angle of the liquid crystal between the first and second substrates is within a range of from 60 degrees to 100 degrees, and the product of the difference of refractive indices of the liquid crystal and the thickness of the liquid crystal is between 150 nm and 330 nm.
In the liquid crystal display device of the present invention, the alignment direction of the liquid crystal layer needs to efficiently orient the linearly polarized light whose plane of vibration varies according to a wavelength, produced by the laminated phase plate of the present invention, in a transmitting direction of the polarizing beam splitter.
The liquid crystal display device {circle around (7)} includes the liquid crystal layer which is capable of increasing the efficiency when the polarizing beam splitter is used and optimized so as to provide a structure satisfying the above-mentioned condition.
Additionally, yet another invention is a liquid crystal display device (liquid crystal display device {circle around (8)}) which is based on the liquid crystal display device {circle around (6)}, and in which the liquid crystal compound has a negative dielectric anisotropy, and the liquid crystal of the liquid crystal layer is aligned in a direction perpendicular to the first and second substrates in the absence of applied voltage.
According to the liquid crystal display device {circle around (8)}, it is possible to provide a display in a normally white mode and achieve a bright display.
Furthermore, yet another invention is a liquid crystal display device (liquid crystal display device {circle around (9)}) which is based on the liquid crystal display device {circle around (8)}, and in which, when the natural pitch of the liquid crystal is denoted by p and the liquid crystal layer thickness is denoted by d, the value of |d/p| is larger than 0 but smaller than 0.5 and the product of the birefringence of the liquid crystal of the liquid crystal layer and the thickness of the liquid crystal layer is between 200 nm and 500 nm.
As a different structure from the liquid crystal display device {circle around (7)}, the liquid crystal display device {circle around (9)} is constructed to have the liquid crystal layer which is capable of increasing the efficiency when the polarizing beam splitter is used and optimized by the liquid crystal alignment of the liquid crystal display device of the present invention.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.